The present invention relates to a paging receiver having a battery saving circuit and, more particularly, to the sync monitoring of such a receiver and the control of the battery saving circuit.
Paging signals developed for use in calling paging receivers include the POCSAG (Post Office Code Standardisation Advisory Group) code as proposed by the British Post Office. The POCSAG code consists of a preamble signal and a number of batches which follow the preamble signal. One batch is made up of a single synchronization codeword (SC) and eight frames each consisting of two codewords and adapted for the transmission of an address codeword or a message codeword. Paging receivers are divided into eight groups such that a receiver belonging to a given one of the eight groups receives and processes only the address codeword of a given frame in each of the batches. For example, a paging receiver which belongs to the second group does not receive and process address codewords except for that one which is contained in the second frames.
Usually, a paging receiver includes a sync monitoring circuit and a battery saving circuit. The sync monitoring circuit in turn includes SC detecting means and means for controlling the battery saving circuit. The sync monitoring circuit monitors SCs in consecutive batches and, when it does not receive an SC in N (e.g. N=2) consecutive batches, detemines that the paging signal has ceased and restores the battery saving circuit to a battery saving mode. In battery saving mode, the receiver enables receiving circuit and related circuitry intermittently so that a preamble signal may be received.
A problem with the prior art sync monitoring circuit as described above is that it has to monitor not only the address codeword in each batch which is assigned to its own group but also an SC. Specifically, while a paging signal is being received, the operation time of the receiving circuit and related circuitry is prolonged by a fraction which is equal to the reception time, resulting in low battery saving efficiency. Another problem is that because the sync monitoring circuit decides that the paging signal has ceased when the SC is not detected within a given, SCs in a following one of a plurality of paging signals which may be transmitted continuously cannot be detected.